Bladder carcinoma induced in animal models by chemical carcinogens in vivo has been demonstrated to correspond in certain features to bladder cancer in man. However, the results of animal studies on carcinogenesis and related phenomena in mammalian bladder urothelium cannot be directly applied to humans unless a means for comparison of responses between animal and man is available. We propose to provide that means by development of an in vitro model of bladder carcinogenesis using normal human bladder urothelium obtained at immediate autopsy. The tumorforming potential of explants displaying morphologic evidence of malignant transformation in vitro can then be tested in vivo by xenotransplantation into the nude athymic mouse. Results can then be compared to observations on animal models in vivo and in vitro. Specific aims of the proposed work are: (1) induction of irreversible neoplastic transformation of normal human bladder in vitro folowing exposure to direct-acting carcinogens. Results will be compared to untreated normal bladder urothelium from the same inidividual. Among the assay systems to be utilized will be morphology by light and electron microscopy, histochemistry, autoradiography of explants labeled with tritiated thymidine, growth in soft agar, and xenotransplantation of carcinogen-treated explants into nude (athymic) mice to evaluate neoplastic potential, and (2) modulation of carcinogenesis by saccharin in vitro in order to examine the role this agent may play during neoplastic transformation of normal human urothelium. Modulation of carcinogenesis will be monitored by light and electron microscopy, histochemistry, autoradiography, growth in soft agar, and xenotransplantation. The results of preliminary experiments described herein demonstrate the feasibility of the proposed studies.